Avalanche forecast

Central Sierra Nevada

Sierra Avalanche Center
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Avalanche danger

Alpine
1 · Low
Treeline
2 · Moderate
Below
2 · Moderate
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Out of date — this forecast expired 11 years ago. You’re viewing past conditions, not the current bulletin.

Highlights

Unusual avalanche conditions persist with pockets of MODERATE avalanche danger in open areas at and below treeline on N-NE-E-SE aspects on slopes 35 degrees and steeper. Persistent slabs associated with the Jan 5 buried surface hoar layer exist in some areas. Where this weak layer is absent, LOW avalanche danger exists. Avoid steep terrain adjacent to areas of recent avalanche activity, even if the crown and debris are covered under a couple inches of new snow and now look old.

Avalanche problems

  • Deep Persistent Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Possible
    Size
    2

    The Jan 5 surface hoar layer buried 1 to 1.5 feet deep in the snowpack has been reactive since Tuesday in the areas where it exists. Buried surface hoar is an uncommon weak layer for this region. This weak layer has been very slow to stabilize. It is now one week old and day to day snowpit data continues to identify ongoing problems. This weak layer is certainly not abiding by any mythical "24 hour rule". Have a look below at the snowpit videos taken from a Level II avalanche class yesterday on Andesite Ridge (Donner Summit area) to see examples of unstable, propagating test results.

    Currently, the areas where avalanches are most likely to be triggered are not in the traditional wind loaded zones along the ridgelines, but in steep open areas at treeline and below treeline on N-NE-E aspects and possibly SE aspects. Have a conversation with your travel partner(s) and make sure everyone understands that this is an at treeline and below treeline problem. Shift the focus from the traditional wind loaded avalanche start zones up high to the steep wind protected open areas lower down on the mountain.

    This weak layer does not exist or is not reactive in all areas. Don't let a lack of evidence of instability in one portion of the forecast area affect how decisions are made when moving to another part of the forecast area. Continue to search out signs of instability including recent avalanche activity, even if it "looks old" buried under an inch or two of recent snowfall. If you see evidence of recent avalanche activity, there is a good chance that the buried surface hoar exists in the area. Snowpit data is very helpful, but it has to come from the right locations and it never proves stability.  If in doubt, stick to slopes less than 32 degrees in steepness. Use an analog inclinometer or smartphone app to measure slope angles rather than guessing.

Avalanche Discussion

Snowpit data made and received from around the forecast area indicates ongoing instability problems in locations where the Jan 5 buried surface hoar layer exists. Where this layer is absent, the snowpack is well bonded and consolidated, with no evidence of instability. Problematic buried surface hoar is known to exist in various locations in the Donner Summit area and in some but not all locations in the Carson Pass area. Observations targeted at finding the Jan 5 buried surface hoar layer over the past few days have indicated an absence of this layer around Barker Pass and Peak (Blackwood Canyon area), on Echo Peak (Echo Summit area), on Jakes Peak (West Shore Tahoe area), and on Mt. Tallac (Desolation Wilderness area). Specific observations have not been made in the Mount Rose area, but no reports of buried surface hoar have been received.

Skier and snowboarder triggered avalanches were reported on Thursday on Andesite Ridge (Donner Summit area) and on Thursday and Friday on Red Lake Peak (Carson Pass area). In both cases avalanches occurred in steep open terrain near treeline to below treeline on NE to E aspects. Snowpack failure occurred 1 to 1.5 below the snow surface at the base of the recent storm snow accumulated since Jan 5.

A few tiny wind deposits were reported yesterday in above treeline terrain. Some skier triggered cracking was noted, but slabs were too small for any dangerous avalanche activity to occur. Some small amount of additional wind transport is possible today above treeline, but significant new wind slab formation is unlikely.

Regions covered